Foot-and-mouth disease virus (FMDV) belongs to the Aphthovirus genus as a member of the Picornaviridae family. FMDV non-enveloped capsid is icosahedral symmetry, which is the classic structural characteristic of the picornavirus family. FMDV capsid composes of 4 structural proteins, VP1, VP2, VP3 and VP4, in which VP1, VP2 and VP3 are surface oriented, whereas VP4 is internal. FMDV elicits acute humoral antibody responses in infected or vaccinated animals, which have been considered to be the most important protective factor against FMD infection. There are increasing numbers of studies discussing about innate immune responses during FMDV infection or vaccination in recent years. FMDV is able to interact with and be internalized by porcine monocyte-derived dendritic cells in a heparin sulfate binding dependent manner. In addition, macrophage phagocytosis of FMDV occurs. Many kinds of pro-inflammatory cytokines and chemokines, such as IL-6, IL-8 and IL-12, are detected in pigs after high potency inactivated FMDV vaccination, suggesting that inactivated FMDV induces monocytic activities.
Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that recognize microbial components and endogenous ligands. Until now, 13 TLRs have been described in mice and 11 in human. When binding to specific ligands, TLRs initiate rapid intracellular signaling pathways involving activation of transcription factor NFκB, MAP kinases and interferon regulatory factors, which result in innate immune activation, including production of pro-inflammatory cytokines, chemokines, interferons and immunoglobulins and co-stimulatory molecules.
Among TLRs, TLR2 recognizes the broadest range of microbial derived agonists, including lipopolysaccharides from different bacterial strains, lipopeptides, lipoarabinomannans, lipomannans, glycosylphosphatidylinositol, lipoteichoic acid, various proteins including lipoproteins and glycoproteins, zymosan and peptidoglycan. TLR2 is also known to involve in virus or viral proteins induced signaling pathway and cytokine production, including Epstein-Barr virus, measles virus, Varicella-Zoster virus, hepatitis B and C virus, human and murine cytomegalovirus, herpes simplex virus, vaccinia virus and lymphocytic choriomeningitis virus. TLR2 can form a heterodimer with either TLR1 or TLR6, and recognizes different ligands by this way. For examples, triacyl lipopeptides and lipoarabinomannan can be recognized by TLR1/2, on the other hand, diacyl lipopeptides, zymosan and lipoteichoic acid can be recognized by TLR2/6. These expansions of ligand specificity cause a broad range of microbial recognition.
The signal transduction pathway mediated by the interaction between a ligand and a TLR is shared among most members of the TLR family and involves a toll/IL-1 receptor (TIR domain), the myeloid differentiation marker 88 (MyD88), IL-1R-associated kinase (IRAK), interferon regulating factor (IRF), TNF-receptor-associated factor (TRAF), TGFβ-activated kinasel, IκB kinases, IκB, and NF-κB. More specifically, for TLRs 1, 2, 4, 5, 6, 7, 8, 9 and 11, this signaling cascade begins with a PAMP ligand interacting with and activating the membrane-bound TLR, which exists as a homo-dimer in the endosomal membrane or the cell surface. Following activation, the receptor undergoes a conformational change to allow recruitment of the TIR domain containing protein MyD88, which is an adapter protein that is common to all TLR signaling pathways except TLR3. MyD88 recruits IRAK4, which phosphorylates and activates IRAK1. The activated IRAK1 binds with TRAF6, which catalyzes the addition of polyubiquitin onto TRAF6. The addition of ubiquitin activates the TAK/TAB complex, which in turn phosphorylates IRFs, resulting in NF-κB release and transport to the nucleus. NF-κB in the nucleus induces the expression of proinflammatory genes.
As a result of their involvement in regulating an inflammatory response, TLRs have been shown to play a role in the pathogenesis of many diseases, including autoimmunity, infectious disease and inflammation. Compositions for modulation of TLR activity are of interest for a variety of purposes, including use as an adjuvant. The present invention addresses this issue.